In recent years, communication utilizing the Internet has been spreading and expanding rapidly in society, because anybody who has at least a personal computer can access a computer on a network only by connecting it to the network. On the other hand, the social problem has become large being accompanied by the spread and expansion of Internet communication where a hacker or a cracker invades a computer system of other people so as to sneak a look at software and data and to carry out falsifying or breakdown thereof.
Speaking of a specific case of unjustified disturbance, first, there is a system disturbance by transmitting a large amount of messages through the network for disturbing the operation of the computer system such that the central system will come not to be used. When the host becomes overloaded owing to this disturbance, it also might happen that the system shuts down.
Also, there is an unjustified disturbance of “unauthorized access and masquerading” by acquiring a password in the host for stealing confidential information, carrying out falsifying and breakdown of information and the like. There is an ugly case in this disturbance such that information possessed by the computer is rewritten arbitrarily so as to deceive a person. Further, also an unjustified activity caused by spyware occurs where a specific personal computer is secretly invaded and personal confidential data such as mail addresses and passwords are exploited. Also, there is a possibility of so-called wiretapping frequently happened to unjustly sneak a look at database contents in the computer connected to the network as mentioned above.
Also, there may occur an action for stealing personal information intentionally in the site or in the managing source of the server and a crisis such as cyber terrorism by a spy lurking within a company or the like.
Further, unjustified disturbance such as feeding “virus” which is a program causing a failure in computers of other people is increasing recently. The personal computers used at home for mails or the like are infected with such fed virus and when it is connected to computers within a company, the whole computers within the company are infected therewith and/or the virus will breakdown files in the computer and furthermore, the whole network may be down.
Therefore, in a communication on the internet utilizing a conventional TCP/IP (Transmission Control Protocol/Internet Protocol) or UDP (User Datagram Protocol), encryption communication called IPsec (IPsec: Security Architecture for Internet Protocol) or SSL (Secure Socket Layer) is utilized as a function for preventing “leakage”, “falsifying” or the like of data.
The feature of IPsec lies not only in merely encrypting specific application but also in encrypting every communication sent from the host at an IP level. In this manner, it becomes possible for a user to have a secure communication without being conscious of the application. Also, IPsec makes it possible to change an encryption algorithm to be used without changing its own structure so that it can be used in the future.
Also, by utilizing SSL, it becomes possible for a client and a server to authenticate each other on the network, and it becomes possible to exchange highly confidential information such as credit card information or the like by encrypting it. In this manner, it is possible to prevent wiretapping of data, resending attack (attack of transmitting data to be flown on the network many times repeatedly by wiretapping), masquerading (communication by masquerading another person himself), falsifying of data and the like.
In the encryption communication used in the present invention, encryption function is added to a TCP layer which is in a transport layer (fourth layer of OSI). The transport layer is a protocol layer for realizing a hypothetical communication path without error between two processes executed on respective nodes. It is possible to send data by the network layer, but there is no guarantee that the data will certainly arrive at a destination. Also, there is no guarantee either that the data will arrive correctly in the sent order. Therefore, it is the transport layer to offer a communication path without error so that it is easy to be used for the application. An example of a communication system resistant against unjustified invasion from outside realized by adding encryption function to the transport layer of the fourth layer was proposed by the present inventors for the first time leading the world and the present inventors named this encryption communication system as “TCP2” (see Patent Document 1).
Patent Document 1 WO2005/015827